Perishable items are now routinely shipped long distances in modern refrigerated vehicles. Although such shipping means work fine for bulk shipments or shipments that can be scheduled in advance to make use of such vehicles, they are not satisfactory for shipping small quantities of demand items that must be delivered within 24 to 48 hours.
At present a shipper who wants to send such demand items must generally use a self-contained refrigerant package. For a refrigerant he must choose between conventional "wet ice" and the reuseable gel-type refrigerant commonly known as "blue ice", or "dry ice" for materials that require or that can withstand very low temperatures. Each of the alternatives has disadvantages, particularly when shipping radiopharmaceuticals that cannot be cooled below -20.degree. C. nor can the temperature be allowed to rise above 3.degree. to 5.degree. C. for periods of 36 or more hours that are at times encountered in transit. "Wet ice" is messy and leakage of the resulting water is possible, thus presenting a possible potential for involvement with goverment regulatory agencies because of the radioactive content of the package. "Blue ice" or refrigerant gel, typically a cellulose gel material in a polyethylene bag or other suitable container that is available commercially, generally provided the required cooling for only up to about 24 hours, which is not satisfactory. "Dry ice" is too cold providing a temperature below -20.degree. C. and also is subject to regulatory problems if significant quantities are required.
Thus, a suitable economical refrigerant that is capable of providing a temperature in the range of from about -20.degree. C. to about 5.degree. C. for 36 or more hours is highly desirable.